A prior art disk drive 10, see FIG. 1, typically includes a main integrated circuit, which is typically called a system on a chip (SOC) 11 that contains many of the electronics and firmware for the drive. Each disk (not shown) can have thin film magnetic material on each of the planar surfaces. Each disk surface normally has a dedicated pair of read and write heads packaged in a slider 13 that also includes fly-height control components. The sliders are mechanically mounted on an actuator (not shown) with various flexible components to allow appropriate degrees of movement during operation. Each slider is a sub-component of a head gimbal assembly (HGA) that typically includes a suspension assembly with a laminated flexure with copper traces to carry the electrical signals to and from the heads.
The sliders are selectively positioned over tracks on the rotating disk by the actuator (not shown). The actuators also provide the electrical connections to the slider components and contain the arm electronics (AE) chip 12 which typically include differential preamplifiers (preamps) 18 for the read heads, write drivers and fly-height controls. Unless otherwise noted, the term actuator will be used herein to include all of the mechanical and electrical components that are required for the sliders to function. A flex cable (not shown) connects the SOC 11 to the AE 12. The AE typically include digital and analog circuitry that control the signals sent to components in the slider and processes the signals received from the slider components. The write driver generates an analog signal that is applied to the inductive coil in the write head to write data by selectively magnetizing portions of the magnetic material on the surface of the rotating disk. Impedance compensation features can be used along the transmission-line path connected to the sensors to compensate for the impedance discontinuities or mismatches (for example, those caused by physical interconnection features) and/or to improve the frequency response of the signal transfer along the transmission line.
The read and write heads (sensors) heads and associated connections are conventionally formed using thin film lithographic patterning in which a series of thin films deposited and patterned on the trailing surface slider. The slider body is typically made of alumina-titanium carbide material. The write head includes an inductive coil. The read head 15 typically includes a magnetoresistive (MR) sensor (read element) located between two magnetic shields. Various subtypes of MR sensors are known including tunnel magnetoresistance (TMR) devices and spin-torque oscillator (STO) devices. In STOs the spin-torque effect generates oscillating magnetization (precession). External magnetic fields can change the oscillation frequency in STOs, so these sensors can be used to read magnetic information recorded in the thin films on the disks.
Reading data at high-data rates from the rotating disks requires a high-bandwidth transmission path. The spin-torque oscillator (STO) requires a very high bandwidth (>3 GHz) to allow for a high-frequency data-modulated carrier frequency. However, the intrinsic read sensor construction creates a significant amount of parasitic capacitance, which limits the bandwidth. The read signal transfer requires a means to mitigate the parasitic capacitance to allow high-frequency signal transfer. Circuit structures that can be fabricated on the slider adjacent to the read sensors are needed to mitigate the parasitic capacitance impact and allow for high-bandwidth signal transfer from the read sensors.
U.S. Pat. No. 6,603,623 to Fontana, et al. (Aug. 5, 2003) describes an inductive magnetic recording (write) head with impedance matching elements including a resistor and capacitor network on the trailing surface of a slider that change the termination impedance of the write head so that it matches the characteristic impedance of the transmission line that supplies the write current.
U.S. Pat. No. 7,545,608 to Araki, et al. (Jun. 9, 2009) uses resistors and capacitors on the trailing surface of a slider to substantially equalize the total parasitic capacitance on the S2 shield with the total parasitic capacitance on the 51 shield, to reduce interference pickup in the high frequency region.
In published U.S. patent application 2013/0135765 (pub. May 30, 2013) Contreras, et al. ladder network compensation circuitry is located on the slider body for increasing the overshoot of the write current at the time of current switching. The ladder network compensation circuitry includes capacitors and inductors fabricated on the slider body, for example, on the trailing surface of the slider adjacent to the write head. Embodiments of discrete capacitors and inductors are described that can be fabricated on the trailing surface of a slider. The inductors include an upper coil section on one side and a lower coil section on the opposite side that are electrically connected by vias.